1. Field of the Invention
Embodiments of the invention generally relate to an apparatus and method for large area substrate processing. In particular, the invention relates to using integrated metrology tools for monitoring and controlling large area substrate processing chambers.
2. Description of the Related Art
Fabrication of semiconductor integrated circuits (IC), flat panel display (FPD) devices, and solar panel devices require processing of multilayer film stacks to create devices, conductors and insulators on a substrate. One example of a multilayer film stack is a thin film transistor (TFT) structure useful for fabricating liquid crystal display (LCD) devices. FIG. 1 (Prior Art) illustrates a cross-sectional schematic view of a thin film transistor structure, which is a common back channel etch (BCE) inverted staggered (or bottom gate) TFT structure. The substrate 101 may comprise a material that is essentially optically transparent in the visible spectrum, such as glass or clear plastic. Typically, for TFT applications, the substrate is a glass substrate with a large surface area, i.e. greater than about 750 cm2. A gate electrode layer 102 is formed on the substrate 101. The gate electrode layer 102 comprises an electrically conductive layer that controls the movement of charge carriers within the TFT. Between the substrate 101 and the gate electrode layer 102, there may be an optional insulating material. A gate dielectric layer 103 is formed on the gate electrode layer 102. A bulk semiconductor layer 104 is formed on the gate dielectric layer 103. A doped semiconductor layer 105 is formed on top of the semiconductor layer 104. The bulk semiconductor layer 104 and the doped semiconductor layer 105 are lithographically patterned and etched using conventional techniques to define a mesa of these two films over the gate dielectric insulator, which also serves as a storage capacitor dielectric. The doped semiconductor layer 105 directly contacts portions of the bulk semiconductor layer 104, forming a semiconductor junction. A conductive layer 106 is then deposited on the exposed surface. Both the conductive layer 106 and the doped semiconductor layer 105 may be lithographically patterned to define source and drain contacts of the TFT. Afterwards, a passivation layer 107 may be deposited. A transparent conductor layer 108 is then deposited and patterned to make contacts with the conductive layer 106.
In general, the substrate for device fabrication is subjected to various processes, such as sputtering, chemical vapor deposition (CVD), physical vapor deposition (PVD), lithography, etching, ion implantation, ashing, cleaning, heating, annealing, and the like in a specific multi-step fabrication sequence to process layers of metal and silicon containing films thereon. For example, the substrate is processed through steps of deposition, patterning, lithography and etching repeated multiple times. Typically, a process chamber is usually configured to deposit a single layer on a substrate. In addition, a number of process chambers can also be coupled together to a central transfer chamber for multi-substrate processing in a multi-substrate processing platform, such as a cluster tool, examples of which are the families of AKT PECVD, PRODUCER®, CENTURA® and ENDURA® processing platforms available from Applied Materials, Inc., of Santa Clara, Calif.
Physical vapor deposition (PVD), or sputtering, is one of the most commonly used processes in devices fabrication. PVD is a plasma process performed in a vacuum process chamber where a negatively biased target with respect to a chamber body or a grounded sputter shield is exposed to a plasma of a gas mixture comprising gases such as inert gases (e.g., argon (Ar)). Bombardment of the target by ions of the inert gas results in ejection of atoms of the target material. In some case, a magnetron is positioned in the back of the target to project a magnetic field parallel to the front side of the target to trap electrons and increase plasma density and sputtering rate. The ejected atoms accumulate as a deposited film on a substrate placed on a substrate pedestal disposed within the process chamber.
Plasma enhanced chemical vapor deposition (PECVD) is generally employed to deposit thin films on a substrate such as a transparent substrate for flat panel display or semiconductor wafer. PECVD is generally accomplished by introducing a precursor gas or gas mixture into a vacuum chamber that contains a substrate. The precursor gas or gas mixture is typically directed downwardly through a distribution plate situated near the top of the chamber. The precursor gas or gas mixture in the chamber is energized (e.g., excited) into a plasma by applying radio frequency (RF) power to the chamber from one or more RF sources coupled to the chamber. The excited gas or gas mixture reacts to form a layer of material on a surface of the substrate that is positioned on a temperature controlled substrate support. Volatile by-products produced during the reaction are pumped from the chamber through an exhaust system.
As the demand for semiconductor, flat panel, and solar panel devices continues to grow, there is a trend to reduce cost by increasing the sizes of the substrates for large scale fabrication. For example, glass substrates utilized for flat panel fabrication, such as those utilized to fabricate computer monitors, large screen televisions, displays for PDAs and cell phones and the like, have increased in size from 550 mm×650 mm to 1500 mm×1800 mm in just a few years and are envisioned to exceed four square meters in the near future. The dimensions of a process chamber or a multi-substrate processing platform have become ever so large.
Substrate mis-processing due to faults in the process chamber could result in scrapping of the substrate, which could have gone through many previous processing steps. Without timely detecting the faults in the process chamber, numerous substrates could be mis-processed and need to be scrapped. For large area substrates, the cost of scrapping these substrates could be substantial. Therefore, it is desirable to monitor and control the substrate processing chamber to ensure targeted substrate processing is properly performed on the substrates to reduce the risk of miss-processing of the substrates.
As a consequence, there is a need for an apparatus and method of monitoring and/or controlling a large area substrate processing chamber.